This invention relates to improvements in remote sensing devices, and to a method of remotely interrogating one or more sensors.
It is known to provide one or more sensing devices which can be deployed in a region that is to be monitored and which can then be interrogated remotely. By remotely interrogated we mean that the sensor device can be interrogated by a suitable monitoring apparatus located a distance away from the sensor device, without physical contact between the monitoring apparatus and the sensor device.
A well known application of remote sensing devices is the tracking of animals in the wild. The animals can be fitted with a radio transmitter which emits a coded electromagnetic (radio frequency) signal. An operator, equipped with a suitable radio receiver and directional antenna can detect the signal from the radio transmitter. The detected signal will be strongest when the antenna is pointed at the radio transmitter, Thus, although a dedicated sensing device is not fitted to the animal along with the radio transmitter the directionality of the signal enables the operator to track the animal across even the most challenging terrain. Information about the location and movement of the animal overtime may be used to learn about the animal's behaviour. Of course, a sensor may be provided along with the radio transmitter, such as a heart rate monitor, and the sensed data can be transmitted by the radio transmitter.
Alternatives to radio transmitter based remote sensing devices include devices which Global Positioning transmitters (GPS). The transmitters send a signal indicating the precise location of the sensing device to a suitable monitoring device. Many commercial vehicles are fitted with tracking devices of this type, and as well as transmitting the location of the vehicle also transmit information about the operating conditions of the vehicle, such as speed, engine revolutions per minute, fluid temperatures and the like. Highly specialised tracking devices are used on racing vehicles to allow the behaviour of the vehicles to be monitored during a race.
In both cases, the remote sensor devices rely on the transmission of radio frequency electromagnetic signals back to a suitable monitoring apparatus. The applicant has appreciated that such signals may not always be effective or desirable. For instance, if the area in which the sensor device is located is electromagnetically noisy, the signal may be swamped. The device may be located in an area in which electromagnetic shielding is present, or perhaps in an area in which it is not acceptable to emit electromagnetic signals. Many scientific experiments can only be carried out in a controlled environment where electromagnetic signals may disrupt the outcome of the experiment. The need to emit a radio signal also has a detrimental effect on battery life of the remote sensor device, limiting the time it can be left in service without maintenance.